Polycurve from Cropviews

Hi evryone!
I’ve got this problem on Dynamo. I create specific elevation views and then i would like to change the crop view by on offset (in my case 450). As in the image below, when i create the polyline offset, it gives me as a result 8 curves for each polyline. For this reason the offset doesnt work but i’m not able to understand why.

Can anyone help me?

Thx so much!